1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and more particularly, to image forming technology for forming an image on a recording medium by using a liquid such as ink.
2. Description of the Related Art
Inkjet recording apparatuses which form a desired image by ejecting ink onto a medium are subject to demands for higher image quality as well as demands for higher image recording speed. These demands are mutually contradictory, and various ways have been contrived in order to resolve these conflicting issues. For example, in cases where a recording medium having permeable characteristics, such as paper, is used, ink droplets permeate into the recording medium and image degradation occurs due to bleeding, dot spreading (shape abnormalities), or the like. Technology is used in which an image is formed provisionally on an intermediate transfer body having non-permeable characteristics, whereupon the image is transferred to a recording medium, thereby suppressing the ink permeation into the recording medium.
Japanese Patent Application Publication No. 10-250052 discloses an invention wherein a primary image is recorded onto an intermediate transfer body by using UV ink which is curable by irradiation of ultraviolet light, the viscosity of the UV ink forming the primary image is increased by radiating ultraviolet light onto the primary image, and the primary image is then transferred onto paper forming a recording medium, thereby making it possible to record a secondary image on the recording medium in a short time.
Japanese Patent Application Publication No. 2005-161603 discloses an inkjet recording method in which a radiation-curable ink is cured on an intermediate transfer body by means of radiation and then the cured ink is transferred by heating at a temperature that is higher than Tg (i.e., the glass transition temperature) of the cured ink.
Japanese Patent Application Publication No. 2001-179960 discloses an inkjet recording apparatus comprising a light irradiation device which is provided inside an intermediate transfer body provided for temporarily holding ink ejected from a recording head (which is also simply referred to as a “head”) and which radiates light curing the ink, wherein the amount (degree) of the light irradiation increases successively, from the ink ejection part onto which the ink is ejected from the head, to the transfer part where the ink is transferred to a recording medium, to the cleaning part where residual ink on the intermediate transfer body is removed.
Japanese Patent Application Publication No. 2005-153368 discloses a composition in which high-viscosity ink of 10000 mPa s or above is applied to a transfer roller by means of a roll coater or blade, an image is then created thereon-using low-viscosity ultraviolet-curable color inkjet ink, and this image is transferred to a printing roller, whereby transferring onto a curved printing medium can be achieved without deteriorating image quality.
However, for instance, when ink droplets ejected from a head onto a medium in order to form an image make contact with each other and combine before fixing on the medium, depositing interference occurs, and hence displacement of the dots formed by the ink and dot shape abnormalities occur, leading to marked deterioration of image quality. This phenomenon is particularly marked in cases of using a medium having non-permeable characteristics (including a medium having an extremely slow permeation speed).
FIG. 16 is a diagram showing a situation of the above-described depositing interference. As shown in FIG. 16, when an ink 32 ejected in the form of a droplet onto an intermediate transfer medium 16 from heads 12C, 12M, 12K, 12Y makes contact with another ink 32 deposited previously onto the intermediate transfer body 16, it is drawn toward the previously deposited ink 32, thus giving rise to beading (combination). If beading of this kind arises, then displacement occurs in the dot formation positions.
In the inventions described in Japanese Patent Application Publication No. 10-250052 and Japanese Patent Application Publication No. 2005-161603, depositing interference is liable to occur if ink droplets make contact with each other before irradiation of ultraviolet light. Moreover, in the invention described in Japanese Patent Application Publication No. 2001-179960, in cases where high-speed printing is performed, depositing interference is liable to occur if ink droplets make contact with each other before light is radiated onto the ink ejection part by the light irradiation device.
Japanese Patent Application Publication No. 2005-153368 does not disclose a method of avoiding depositing interference of the color ink ejected in the form of droplets by the inkjet head. If the viscosity of the previously applied high-viscosity ink is too high, then it is difficult for the low-viscosity color ink to penetrate into the film of high-viscosity ink, and hence depositing interference is liable to occur when the color ink is deposited. Furthermore, in order to put a high-viscosity ink having a viscosity of 10000 mPa·s or above onto a transfer roller, it is necessary to apply the ink to the whole surface of the transfer roller by means of a roll coater, blade, or the like, and therefore the consumption of high-viscosity ink rises.